The present invention relates to a magnetic resistor sensor and a magnetic encoder using such a sensor, and more particularly relates to improvements in universality and structural simplicity of a magnetic encode used for detection of various displacements in automatic devices such as industrial robots.
A magnetic-resistor is in general made up of a magnetic scale coupled to a mobile object and one or more magnetic sensors combined with each other for relative sensing displacement of the object.
The magnetic scale includes a magnetic information pattern magnetized on a magnetic medium along an elongated track. Most commonly, the magnetic medium is circular in shape, the track is annular and the magnetic information pattern is given in the form of sine waves of a prescribed pitch, i.e. a prescribed wave length (.lambda.).
The magnetic sensor usually takes the form of a magnetic-resistor sensor made of a material which changes its inherent resistance depending upon the intensity of the magnetic field applied thereto. The magnetic-resistor sensor has a comb-like pattern which is formed on a base plate and made up of a plurality of sensor sections and a plurality of connector sections each intervening between adjacent sensor sections. The sensor sections run normal to the direction of relative displacement and the connector sections run parallel to the direction of relative displacement between the magnetic scale and the magnetic sensor. The sensor sections are spaced from each other in the direction of relative displacement depending on the above-described pitch of the magnetic information pattern stored on the magnetic scale.
As the relative displacement advances, the magnetic information pattern on the magnetic scale is detected by the magnetic sensor which in turn generates corresponding output signals.
As stated above, a magnetic resistor sensor takes the form of a comb-like pattern formed on a base plate in which sensor sections are spaced from each other depending on the pitch of a magnetic information pattern stored on a counterpart magnetic scale. Thus, a magnetic-resistor sensor of a specified sensor section pitch can be used only for a magnetic scale of a corresponding magnetic-resistor sensor is unusable for a magnetic scale of a different magnetic information pattern pitch. Thus, most conventional magnetic resistor sensors are have in poor universatility.
In detection of a displacement of a mobile object by a magnetic encoder, a magnetic information pattern stored on a magnetic scale is sequentially detected by an associated magnetic-resistor sensor (or sensors) during a relative displacement and the magnetic encoder generates absolute position data indicative of the amount of displacement of the mobile object. Each absolute position datum is usually made up of first and second fractions. The first fraction indicates the current number of magnetic domains on the magnetic scale which have been passed by the magnetic resistor sensor, the second fraction indicates the current position of the magnetic-resistor sensor in a particular magnetic domain on the magnetic scale. The magnetic encoder is provided with an electric circuit which processes output signals from the magnetic-resistor sensor for generation of the first and second fractions of the absolute position data. Such as electric circuit includes a counter which must be reset every time a border between adjacent magnetic domains on the magnetic scale is passed by the magnetic-resistor sensor during the relative displacement. To this end, the magnetic scale needs to include, in addition to a first track for storing the magnetic information pattern, a second track for storing a magnetic reference position pattern which shows the borders between adjacent magnetic domains. Use of such an additional track requires an increased size of the magnetic scale and provision of an additional magnetic-resistor sensor for detecting such a magnetic reference position pattern on the magnetic scale.